Driver side airbag modules, which include an airbag cushion and an airbag module cover, are normally positioned within a hub of a steering wheel of a motor vehicle. The hub of the steering wheel also happens to be the same area which conventionally includes a horn switch assembly. Accordingly, the airbag module cover must additionally serve to actuate the horn switch. A horn switch assembly normally includes a horn switch and a backing plate attached to an inner surface of a horn actuation face of the airbag module cover. The horn switch and backing plate are usually attached to the inner surface by ultrasonic welding or heat staking.
Many horn switch assemblies include a membrane horn switch. Membrane switches conventionally comprise two very thin sheets having conductive coatings thereon which are normally separated by thin spacers. Pressure on the switch pushes the conductive surfaces together to close a circuit and actuate the horn. Normally, a plurality of force concentrators are positioned on the inner surface of the horn actuation area of the airbag module cover to transfer driver applied pressure more efficiently to the horn switch.
Some horn switch assemblies include a bend sensor horn switch that includes a bend sensitive variable resistance circuit. The resistance of the variable resistance circuit measurably changes as it is bent and the variable resistance circuit is connectable to a horn control circuit that responds to extremely rapid changes in resistance but not to more gradual changes caused by, for example, temperature variations or close packing of the horn switch within the airbag module. Normally, a plurality of force concentrators are positioned on the inner surface of the horn actuation area of the airbag module cover and a plurality of supports are positioned on the backing plate. The force concentrators and supports are arranged to bend the variable resistance circuit in preferably only one axis or direction. In addition, the force concentrators and supports are provided in the form of elongated ribs for translating a localized driver-applied force over a greater area of the bend sensor.
Mounting the horn switch assembly to the airbag module cover by ultrasonic welding or heat staking has been found to be a time consuming assembly process that increases the cost of manufacturing the airbag module. In addition, the horn switch is sometimes damaged by heat staking, requiring the replacement of the horn switch and airbag module cover. A horn switch assembly welded to the airbag module cover requires replacing the entire airbag module cover when replacing damaged or defective horn switches. Furthermore, heat staking puts constraints on the design, material and manufacture of the airbag module cover.
One alternative to mounting the horn switch assembly by heat staking or welding is to provide a horn switch pocket in the airbag module for receiving and holding the horn switch assembly against the inner surface of the horn actuation area of the airbag module cover. An example of such a horn switch pocket is shown and described in co-pending application Ser. No. 08/587,855 filed Jan. 11, 1996 (Attorney's Docket Number 30932100.173).
There is, therefore, a need for a horn switch assembly that is adapted to be mounted in a horn switch pocket of an airbag module. There is a further need for the horn switch assembly to be provided in embodiments incorporating a membrane horn switch and a bend sensor horn switch.